typeMismatch.java.util.List when trying to set a list

I was able to recreate your error case using a form validation. You are probably trying to pass a form data that is [5, 3] for the tags variable with type List<Long>, but passing with brackets break that structure, the value ought to be 5, 3...

So what I've done is;

1. Create a dummy controller using your input;

   @Controller
   public class TestController {
   
       @PostMapping
       public ModelAndView test(@Validated @ModelAttribute final PrmBcClipInsert prmBcClipInsert, final BindingResult bindingResult) {
           final ModelAndView modelAndView = new ModelAndView();
           System.out.println(prmBcClipInsert.getTags());
           modelAndView.setViewName("test");
           return modelAndView;
       }
   }
   

2. Pass the form with tags=[5,3], and get the following error in BindingResult;

   org.springframework.validation.BeanPropertyBindingResult: 1 errors Field error in object 'prmBcClipInsert' on field 'tags': rejected value [[5, 3]]; codes [typeMismatch.prmBcClipInsert.tags,typeMismatch.tags,typeMismatch.java.util.List,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [prmBcClipInsert.tags,tags]; arguments []; default message [tags]]; default message [Failed to convert property value of type 'java.lang.String' to required type 'java.util.List' for property 'tags'; nested exception is java.lang.NumberFormatException: For input string: "[5,3]"]

   Which is the identical error that you were getting... So I presume either you get this PrmBcClipInsert as a form input like in my example, or you are trying to do a similar binding in some other part of your code...

3. Pass the form with tags=5,3, no error...

---

There can be a custom converter to support for passing said array input with brackets in binding logic with something like;

@Component
public class LongListConverter implements Converter<String, List<Long>> {

    @Override
    public List<Long> convert(String source) {
        return Arrays.stream(StringUtils.strip(source, "[]").split(","))
                .map(StringUtils::strip)
                .map(Long::new)
                .collect(Collectors.toList());
    }
}

With this, both 5, 3 & [5, 3] can be supplied as value of tags variable.